The Affordable Care Act isn’t the only consequential law whose fate the U.S. Supreme Court holds in its hands. Before the end of the month, the court is also expected to decide whether to hear a Montana campaign-finance case that may alter the landmark Citizens United ruling.

The Montana case, American Tradition Partnership v. Bullock, arose from a challenge to the state’s campaign-finance law. In 1912, when Montana’s “copper kings” routinely drew on their immense wealth to buy off local politicians, the state’s citizens approved a ballot initiative called the Corrupt Practices Act, which banned corporate money in state campaigns and imposed strict limits on individual donations. Today state legislators can take no more than $160 from individual donors; candidates for governor can take about $1,000. The winner of a Montana senate race spends an average of $17,000 — compare that with the $125 million–plus that’s been spent in Wisconsin on a series of recall elections since last winter. Montana’s insistence on transparency and the barriers it built to contain corporate spending have “nurtured a rare, pure form of democracy,” wrote Brian Schweitzer, the state’s Democratic governor, in an op-ed this month.

But such democracies have been upended by Citizens United, the 2010 U.S. Supreme Court ruling that held that political spending by corporations and unions is protected speech under the First Amendment. Wielding the case as a precedent, American Tradition Partnership — a Virginia-based conservative advocacy group devoted to “fighting the radical environmentalist agenda” — filed suit to strike down Montana’s statutes, which the group argued violate the spirit of Citizens United. A district court agreed with it. But as Montana’s recent nullification movement illustrates, many locals are happy to flout federal precedent when it comes to laws they don’t like. Last December, Montana’s supreme court upheld the 100-year-old law.

Now the U.S. Supreme Court is being asked to reverse that decision. Twenty-two states, plus the District of Columbia, have joined Montana in arguing that “states should have the right to be the masters of their own elections,” as Montana attorney general Steve Bullock — who is also the state’s Democratic nominee to replace Schweitzer — wrote in an op-ed on Monday. But that contention appears to fly in the face of Citizens United, as one of the dissenting justices on the Montana supreme court ruefully pointed out, while lamenting “the distasteful position of having to defend the applicability of a controlling precedent with which I profoundly disagree.”

Soon the U.S. Supreme Court will decide whether to hear the case, or to issue a summary reversal, which would overturn the lower court’s ruling. It’s “pretty much a sure thing” that they will opt to hear it, argued New York Times legal analyst Adam Liptak. (Four Supreme Court Justices are required to grant certiorari, compared with five to issue a summary judgment, meaning the court’s liberal bloc has the power to force a hearing.) Justices took up the issue on June 14, and are slated to discuss it again this week, meaning a decision could come as early as June 25. Trumpeted by liberals and advocates of stricter campaign-finance regulations, the matter has mushroomed into “perhaps the most serious challenge to date to the Citizens United decision,” wrote the Nation‘s Katrina vanden Heuvel.

But most legal scholars agree that if the court opts to hear the case, it is highly unlikely to reverse course and ban corporate campaign spending. While the Justices could issue a narrowly tailored ruling, they could also further cement the established precedent. “If you’re a liberal Justice and you don’t like Citizens United, it’s not at all clear that the right thing to do is to grant cert, because the court could make things worse. There’s no reason to believe that Justice Kennedy or the other Justices have changed their mind about the wisdom of Citizens United, and therefore it might be foolish to have the court hear the case,” says Richard Hasen, a professor of election law and campaign-finance regulation at the University of California at Irvine. “Be careful what you wish for. I’m not sure why these liberal groups are urging the court to take the case.”

Bullock, the Montana attorney general spearheading the challenge, says he is pursuing the case to defend a law that has benefited the state for a century. “For a century, Montana’s Corrupt Practices Act has ensured the integrity of our state and local elections. That law deserves its day to be heard before our nation’s highest court,” he said in a statement on Monday, which contended that at this point, there is “little point in speculating as to what the court will ultimately decide.”

If the polarized court opts to take the case, it would set up a pivotal showdown over a law that has reshaped U.S. politics, including a presidential race in which conservative super PACs are pouring cash into the fight to oust Barack Obama. Given the conservative bent of the John Roberts court, this is a fight that liberals are likely to lose.

In a fitting twist, that defeat could coincide with another one. As Tom Goldstein of SCOTUSblog points out, should the court take the case, a decision could come on Nov. 6, 2012 — Election Day.